local csv = require "ftcsv"
local datafile = require "datafile"
local dir = require "pl.dir"
local etlua = require "etlua"
local json = require "cjson"
local markdown = require "markdown"
local path = require "pl.path"
local pp = require "pl.pretty"

local nsm = require "volksdata.namespace"
local term = require "volksdata.term"
local triple = require "volksdata.triple"
local graph = require "volksdata.graph"

local pkar = require "pocket_archive"
local logger = pkar.logger
local model = require "pocket_archive.model"
local repo = require "pocket_archive.repo"
local get_single_v = repo.get_single_v
local transformers = require "pocket_archive.transformers"

local dbg = require "debugger"


-- "nil" table - for missing key fallback in chaining.
local NT = {}

-- Extension for type-based icon files.
local ICON_EXT = ".svg"

local asset_dir = pkar.config.htmlgen.out_dir
local index_path = path.join(asset_dir, "js", "fuse_index.json")
local keys_path = path.join(asset_dir, "js", "fuse_keys.json")
local idx_ignore = {first = true, next = true}
-- Collector for all search term keys.
local idx_keys

-- HTML templates. Compile them only once.
-- TODO Add override for user-maintained templates.
local templates = {
    idx     = {file = "index.html"},
    coll    = {file = "coll.html"},
    dres    = {file = "dres.html"},
    ores    = {file = "ores.html"},
    head    = {file = "head_common.html"},
    header  = {file = "header.html"},
}
for _, tpl in pairs(templates) do
    local fh = datafile.open(path.join("templates", tpl.file))
    tpl.data = assert(etlua.compile(fh:read("a")))
end


-- HTML generator module.
local M = {
    res_dir = path.join(pkar.config.htmlgen.out_dir, "res"),
    asset_dir = asset_dir,
    icon_dir = path.join(asset_dir, "icons"),
    media_dir = path.join(pkar.config.htmlgen.out_dir, "media"),
    webroot = "",  -- TODO switch depending on local FS or webserver generation.
}

local MEDIA_WEB_PATH = M.media_dir:gsub(pkar.config.htmlgen.out_dir, "")
local TN_FS_PATH = path.join(M.media_dir, "thumbnail")
local TN_WEB_PATH = TN_FS_PATH:gsub(pkar.config.htmlgen.out_dir, "")


-- Get model configuration from subject URI.
local function get_mconf(s)
    local ctype = get_single_v(s, "content_type")

    return model.types[model.uri_to_id[nsm.denormalize_uri(ctype.data)]]
end


local function get_breadcrumbs(mconf)
    -- Breadcrumbs, from top class to current class.
    -- Also verify if it's a File subclass.
    local breadcrumbs = {}
    for i = 1, #mconf.lineage do
        breadcrumbs[i] = {
            mconf.lineage[i],
            model.types[mconf.lineage[i]].label
        }
    end

    return breadcrumbs
end


--[[ Infer thumbnail web path from the resource subject URI.

    If the resource is not a file and as such does not have a thumbnail of
    its own, traverse the list of first children and use the first one found
    with a thumbnail.

    @param[in] s Subject (resource) URI.

    @param[in] ext Optional extension to add, including the extension separator
    (`.`). If not provided, `.jpg` is used.
--]]
local function get_tn_url(s, ext)  -- TODO caller needs to pass correct ext
    if repo.gr:contains(triple.new(s, pkar.RDF_TYPE, model.id_to_uri.file))
    then
        -- The subject is a file.
        return pkar.gen_pairtree(TN_WEB_PATH, s.data, ext or ".jpg", true)
    end

    -- If it's a brick, look for its ref.
    local ref = get_single_v(s, "ref")
    if ref then return get_tn_url(ref, ext) end

    local pref_rep = get_single_v(s, "pref_rep")
    if pref_rep then return get_tn_url(pref_rep, ext) end

    -- Recurse through all first children until one with a thumbnail, or a
    -- leaf without children, is found.
    -- Look for preferred rep first.
    local t = get_single_v(s, "pref_rep")
    if not t then
        -- If not found, look for reference of first child.
        t = get_single_v(s, "first")
        if t then t = get_single_v(t, "ref") end
    end
    if t then return get_tn_url(t, ext) end
end


--[[ Find closest available type icon to the given type.
--]]
local function get_icon_url(lineage)
    for i = #lineage, 1, -1 do
        if path.isfile(path.join(M.icon_dir, lineage[i] .. ICON_EXT)) then
            return M.webroot .. "/icons/" .. lineage[i] .. ICON_EXT
        end
    end
end


local function generate_coll(s, mconf)
    local pref_rep = get_single_v(s, "pref_rep")

    local members = {}
    local child_s = get_single_v(s, "first")
    --[[ FIXME this should check for the ref attribute of the proxy.
    if not repo.gr:contains(triple.new(
        s, model.id_to_uri.has_member, first
    )) then
        error(("first child %s is not a member of %s!")
            :format(first.data, s.data)
        )
    end
    --]]

    -- First child is the alternative pref representation.
    if not pref_rep then pref_rep = child_s end

    local pref_rep_url
    if pref_rep then
        pref_rep_url = pkar.gen_pairtree("/res", pref_rep.data, ".html", true)
        -- Collection page uses full size image, shrunk to size if necessary.
        pref_rep_file = get_tn_url(pref_rep):gsub(TN_WEB_PATH, MEDIA_WEB_PATH)
    end

    local child_ref, child_label, child_mconf
    while child_s do
        child_ref = get_single_v(child_s, "ref")
        -- Skip relationship with long description doc.
        if repo.gr:contains(
            triple.new(s, model.id_to_uri.long_description, child_ref)
        ) then goto skip end
        child_mconf = get_mconf(child_ref)
        --if not child_ref then child_ref = child_s end
        child_label = get_single_v(child_s, "label")
        if not child_label then
            if child_mconf.types.file then
                child_label = path.basename(
                        get_single_v(child_ref, "source_path").data)
            else
                child_label = get_single_v(child_ref, "label")
            end
        end
        if child_label.data then child_label = child_label.data end
        table.insert(members, {
            icon = get_icon_url(child_mconf.lineage),
            tn = get_tn_url(child_s),
            href = pkar.gen_pairtree("/res", child_ref.data, ".html", true),
            label = child_label,
            ctype_label = child_mconf.label,
        })

        ::skip::
        child_s = get_single_v(child_s, "next")
    end

    local title = get_single_v(s, "label")
    local description = get_single_v(s, "description")
    local body_rel = get_single_v(s, "long_description")

    local body
    if body_rel then
        local body_res_path = get_single_v(body_rel, "archive_path").data
        local bfh = assert(io.open(body_res_path, "r"))
        body = markdown(bfh:read("a"))
        bfh:close()
    end

    out_html = templates.coll.data({
        --webroot = M.webroot,
        site_title = pkar.config.site.title,
        title = title.data,
        description = description.data,
        body = body,
        head_tpl = templates.head.data,
        header_tpl = templates.header.data,
        mconf = mconf,
        uri = s,
        members = members,
        tn_url = get_tn_url(s),
        pref_rep = {
            url = pref_rep_url,
            file = pref_rep_file,
        },
        icon_url = get_icon_url(mconf.lineage),
        --breadcrumbs = get_breadcrumbs(mconf),
        rdf_href = pkar.gen_pairtree("/res", s.data, ".ttl", true),
    })

    local res_path = pkar.gen_pairtree(M.res_dir, s.data, ".html")
    local ofh = assert(io.open(res_path, "w"))
    ofh:write(out_html)
    ofh:close()

   return true
end


local function generate_dres(s, mconf)
    local dmd = {}
    local rel = {}
    local children = {}
    local title
    -- Metadata
    local attrs = repo.gr:connections(s, term.LINK_OUTBOUND)

    local pref_rep = get_single_v(s, "pref_rep")
            or get_single_v(s, "has_member")

    for p, ots_it in attrs:iter() do
        local pname = model.uri_to_id[nsm.denormalize_uri(p.data)] or p.data
        logger:debug("DRES pname: " .. pname)
        local pconf = ((mconf.properties or NT)[pname] or NT)
        -- RDF types are shown in in breadcrumbs.
        if pname == pkar.RDF_TYPE.data then goto skip end
        if pname == "first" then
            -- Build a linked list for every first found.
            for o in ots_it do
                -- Loop through all first children.
                local child_s = o
                if not pref_rep then pref_rep = child_s end

                logger:debug("local child_s: ", child_s.data)
                local ll = {}

                -- Fallback labels.
                local label
                local ref = get_single_v(child_s, "ref")
                if ref then
                    label = (get_single_v(ref, "label") or NT).data
                else
                    label = (get_single_v(child_s, "label") or NT).data
                end
                if not label then
                    label = (get_single_v(child_s, "source_path") or NT).data
                    if label then label = path.basename(label)
                    else label = child_s.data end
                end

                while child_s do
                    -- Loop trough all next nodes for each first child.
                    local ref = get_single_v(child_s, "ref")
                    table.insert(ll, {
                        href = pkar.gen_pairtree("/res", ref.data, ".html", true),
                        label = label,
                        tn = get_tn_url(ref),
                    })
                    child_s = get_single_v(child_s, "next")
                end
                table.insert(children, ll)
            end
        elseif pname == "next" then
            -- Sibling.
            for o in ots_it do ls_next = o.data break end
        elseif pconf.type == "resource" then
            -- Relationship.
            rel[pname] = {
                label = pconf.label,
                description = pconf.description,
                uri = pconf.uri,
            }
            for o in ots_it do
                table.insert(rel[pname], {
                    href = pkar.gen_pairtree("/res", o.data, ".html", true),
                    label = nsm.denormalize_uri(o.data),
                })
            end
        else
            -- Descriptive metadata.
            local attr = {
                label = pconf.label or pname,
                description = pconf.description,
                uri = pconf.uri,
            }
            -- TODO differentiate term types
            for o in ots_it do table.insert(attr, o.data) end
            table.sort(attr)
            if p == model.id_to_uri.label then title = attr[1] end
            table.insert(dmd, attr)
        end
        ::skip::
    end
    table.sort(
        dmd, function(a, b)
            return ((a.label or a.uri) < (b.label or b.uri))
        end
    )
    table.sort(rel)
    table.sort(children)
    logger:debug("Lineage:", pp.write(mconf.lineage))
    logger:debug("DMD:", pp.write(dmd))
    logger:debug("REL:", pp.write(rel))
    logger:debug("Children:", pp.write(children))
    logger:debug("Breadcrumbs:", pp.write(get_breadcrumbs(mconf)))

    local pref_rep_url
    if pref_rep then
        pref_rep_url = pkar.gen_pairtree("/res", pref_rep.data, ".html", true)
        pref_rep_file = get_tn_url(pref_rep):gsub(TN_WEB_PATH, MEDIA_WEB_PATH)
    end

    out_html = templates.dres.data({
        --webroot = M.webroot,
        site_title = pkar.config.site.title,
        title = title or s.data,
        head_tpl = templates.head.data,
        header_tpl = templates.header.data,
        mconf = mconf,
        uri = s,
        dmd = dmd,
        rel = rel,
        children = children,
        ls_next = ls_next,
        tn_url = get_tn_url(s),
        pref_rep = {
            url = pref_rep_url,
            file = pref_rep_file,
        },
        icon_url = get_icon_url(mconf.lineage),
        breadcrumbs = get_breadcrumbs(mconf),
        rdf_href = pkar.gen_pairtree("/res", s.data, ".ttl", true),
    })

    local res_path = pkar.gen_pairtree(M.res_dir, s.data, ".html")
    local ofh = assert(io.open(res_path, "w"))
    ofh:write(out_html)
    ofh:close()

   return true
end


local function generate_ores(s, mconf)
    local techmd = {}
    local rel = {}
    -- Metadata
    local attrs = repo.gr:connections(s, term.LINK_OUTBOUND)
    for p, ots_it in attrs:iter() do
        local pname = model.uri_to_id[nsm.denormalize_uri(p.data)] or p.data
        local pconf = ((mconf.properties or NT)[pname] or NT)
        -- RDF types are shown in in breadcrumbs.
        if pname == pkar.RDF_TYPE.data then goto skip end
        if pname == "next" then
            -- Sibling.
            for o in ots_it do ls_next = o.data break end
        elseif pconf.type == "resource" then
            -- Relationship.
            rel[pname] = {
                label = pconf.label,
                description = pconf.description,
                uri = pconf.uri,
            }
            for o in ots_it do
                table.insert(rel[pname], {
                    href = pkar.gen_pairtree("/res", o.data, ".html", true),
                    label = nsm.denormalize_uri(o.data),
                })
            end
        else
            -- Descriptive metadata.
            techmd[pname] = {
                label = pconf.label,
                description = pconf.description,
                uri = pconf.uri,
            }
            -- TODO differentiate term types
            for o in ots_it do table.insert(techmd[pname], o.data) end
            table.sort(techmd[pname])
        end
        ::skip::
    end
    table.sort(techmd)
    table.sort(rel)
    logger:debug("Lineage:", pp.write(mconf.lineage))
    logger:debug("Breadcrumbs:", pp.write(get_breadcrumbs(mconf)))
    logger:debug("techmd:", pp.write(techmd))
    logger:debug("REL:", pp.write(rel))

    -- Transform and move media assets.
    local dest_fname, dest_dir, dest  -- Reused for thumbnail.
    logger:debug("Transforming resource file.")
    local res_path = techmd.archive_path
    if not res_path then error("No file path for File resource!") end
    local txconf = (mconf.gen or NT).transformers or {}

    local pres_conf = txconf.pres or {fn = "copy"}
    -- Set file name to resource ID + source extension.
    dest_fname = (
            s.data:gsub(nsm.get_ns("par"), "") ..
            (pres_conf.ext or path.extension(res_path[1])))
    dest_dir = path.join(
            M.media_dir, dest_fname:sub(1, 2), dest_fname:sub(3, 4))
    dest = path.join(dest_dir, dest_fname)
    assert(transformers[pres_conf.fn](
            res_path[1], dest, table.unpack(pres_conf or NT)))
    local pres = dest:gsub(pkar.config.htmlgen.out_dir, "")
    logger:debug("Presentation file: ", pres)

    -- Thumbnail.
    local tn
    if txconf.thumbnail then
        if txconf.thumbnail.ext then
            dest_fname = path.splitext(dest_fname) .. txconf.thumbnail.ext
        end
        dest = pkar.gen_pairtree(TN_FS_PATH, dest_fname)
        assert(transformers[txconf.thumbnail.fn](
                res_path[1], dest, table.unpack(txconf.thumbnail or NT)))
        tn = dest:gsub(M.media_dir, TN_WEB_PATH)
        logger:debug("Thumbnail: ", tn)
    end

    out_html = templates.ores.data({
        --webroot = M.webroot,
        site_title = pkar.config.site.title,
        fname = path.basename(techmd.source_path[1]),
        head_tpl = templates.head.data,
        header_tpl = templates.header.data,
        mconf = mconf,
        uri = s,
        techmd = techmd,
        rel = rel,
        ls_next = ls_next,
        icon_url = get_icon_url(mconf.lineage),
        breadcrumbs = get_breadcrumbs(mconf),
        pres = pres,
        thumbnail = tn,
        rdf_href = pkar.gen_pairtree("/res", s.data, ".ttl", true),
    })

    local res_path = pkar.gen_pairtree(M.res_dir, s.data, ".html")
    local ofh = assert(io.open(res_path, "w"))
    ofh:write(out_html)
    ofh:close()

   return true
end


M.generate_search_idx = function(s, mconf)
    local rrep = {
        id = s.data:gsub("^.*/", ""),
        tn = get_tn_url(s),
        href = pkar.gen_pairtree("/res", s.data, ".html", true),
        content_type = mconf.id,
        type = mconf.lineage,
        icon = get_icon_url(mconf.lineage),
    }

    local function format_value(pname, o)
        logger:debug("Adding value to " .. pname .. ": " .. ((o or NT).data or "nil"))
        local v
        if pname == "type" or pname == "content_type" then
            v = model.uri_to_id[p]
        else v = o.data
        end
        return v
    end

    local attrs = repo.gr:connections(s, term.LINK_OUTBOUND)
    local fpath

    for p, ots_it, ots_size in attrs:iter() do
        local pname
        if p == model.id_to_uri.content_type then goto skip end
        if p == model.id_to_uri.source_path then
            if mconf.types.file then
                fpath = ots_it()
                rrep.fname = path.basename(fpath.data)
            end
            goto skip
        end
        pname = model.uri_to_id[nsm.denormalize_uri(p.data)]
        if not pname then goto skip end
        local pconf = (mconf.properties or NT)[pname] or NT
        -- TODO dereference & index resource values.
        if idx_ignore[pname] or pconf.type == "resource" then goto skip end

        local attr
        -- Quick check if it's multi-valued
        if ots_size > 1 then
            attr = {}
            for o in ots_it do
                table.insert(attr, format_value(pname, o))
            end
        else
            attr = format_value(pname, ots_it())
        end

        rrep[pname] = attr  -- Add to search index.
        idx_keys[pname] = true  -- Add to search keys.
        ::skip::
    end
    return rrep
end


M.generate_ll = function(s)
    local res_gr = repo.get_rsrc(s)
    local mconf = get_mconf(s)

    local tdata = {
        {
            id = path.basename(s.data),
            content_type = mconf.id,
        },
    }
    for p, ots_it in pairs(res_gr:connections(s, term.LINK_OUTBOUND)) do
        local pname = model.uri_to_id[nsm.denormalize_uri(p.data)]
        --if p == pkar.RDF_TYPE then goto skip_p end
        if not pname then goto skip_p end
        if pname == "content_type" then goto skip_p end
        for o in ots_it do
            -- Find a row where the pname slot has not been occupied.
            if (mconf.properties[pname] or {}).type == "resource" then
                o = {data = o.data:gsub(nsm.get_ns("par"), "")}
            end
            for i = 1, math.huge do
                if (tdata[i] or NT)[pname] then goto continue
                else
                    if tdata[i] then tdata[i][pname] = o.data
                    else tdata[i] = {[pname] = o.data} end
                    break
                end
                ::continue::
            end
        end
        ::skip_p::
    end
    -- FIXME ftcsv encodes nil values as `"nil"`. See
    -- https://github.com/FourierTransformer/ftcsv/issues/46

    return csv.encode(tdata, {encodeNilAs = ""})
end


M.generate_resource = function(s)
    local res_type
    res_type = get_single_v(s, "content_type")
    local mconf = model.from_uri(res_type)

    -- Generate RDF/Turtle doc.
    local res_path = pkar.gen_pairtree(M.res_dir, s.data, ".ttl")
    dir.makepath(path.dirname(res_path))
    local ofh = assert(io.open(res_path, "w"))
    for chunk in repo.serialize_rsrc(s, "ttl") do ofh:write(chunk) end
    ofh:close()

    -- Generate HTML doc.
    if mconf.types.collection then assert(generate_coll(s, mconf))
    elseif mconf.types.file then assert(generate_ores(s, mconf))
    else assert(generate_dres(s, mconf)) end

    -- Generate JSON rep and append to search index.
    idx_rep = M.generate_search_idx(s, mconf)
    json_rep = "  " .. json.encode(idx_rep)
    ofh = assert(io.open(index_path, "a"))
    ofh:write(json_rep)
    ofh:write(",\n")  -- Hack together the JSON objects in a list.
    ofh:close()

    return s
end


M.generate_resources = function(coll_id)
    -- TODO It's more complicated than this. Each member in the collection
    -- must be scanned recursively for outbound links and visited links must
    -- be noted down to avoid loops.
    --[[
    if coll_id then
        subject_ts = repo.gr:term_set(
            term.new_iriref_ns("par:" .. coll_id), triple.POS_S,
            model.id_to_uri.has_member, triple.POS_P
        )
    else subjects_ts = repo.gr:unique_terms(triple.POS_S) end
    --]]
    subjects_ts = repo.gr:unique_terms(triple.POS_S)

    -- Initialize the JSON template with an opening brace.
    local ofh = assert(io.open(index_path, "w"))
    ofh:write("[\n")
    ofh:close()

    -- TODO parallelize
    for s in subjects_ts:iter() do assert(M.generate_resource(s)) end

    -- Close the open list brace in the JSON template after all the resources
    -- have been added.
    ofh = assert(io.open(index_path, "a"))
    ofh:write("  {}\n]")  -- Add empty object to validate the last comma
    ofh:close()

    -- Write index keys.
    ofh = assert(io.open(keys_path, "w"))
    idx_keys_ls = {}
    for k in pairs(idx_keys) do table.insert(idx_keys_ls, k) end
    ofh:write(json.encode(idx_keys_ls))
    ofh:close()

    return true
end


M.generate_homepage = function()
    local idx_data = {objects = {}, collections = {}}
    -- Get all subject of type: Artifact.
    local s_ts = repo.gr:term_set(
        pkar.RDF_TYPE, triple.POS_P,
        term.new_iriref_ns("pas:Artifact"), triple.POS_O
    )
    local i = 1
    for s in s_ts:iter() do
        if i > (pkar.config.htmlgen.max_homepage_items or 10) then break end

        table.insert(idx_data.objects, {
            href = pkar.gen_pairtree("/res", s.data, ".html", true),
            title = get_single_v(s, "label"),
            submitted = get_single_v(s, "submitted").data,
            tn = get_tn_url(s),
        })
        i = i + 1
    end
    table.sort(
        idx_data.objects, function(a, b)
            return a.submitted < b.submitted end
    )

    s_ts = repo.gr:term_set(
        pkar.RDF_TYPE, triple.POS_P,
        term.new_iriref_ns("pas:Collection"), triple.POS_O
    )
    for s in s_ts:iter() do
        table.insert(idx_data.collections, {
            href = pkar.gen_pairtree("/res", s.data, ".html", true),
            title = get_single_v(s, "label"),
            submitted = get_single_v(s, "submitted").data,
            tn = get_tn_url(s),
        })
    end
    table.sort(
        idx_data.collections, function(a, b)
            return a.submitted < b.submitted end
    )

    logger:debug(pp.write(idx_data))

    out_html = templates.idx.data({
        webroot = M.webroot,
        site_title = pkar.config.site.title,
        head_tpl = templates.head.data,
        header_tpl = templates.header.data,
        nsm = nsm,
        idx_data = idx_data,
    })

    local idx_path = path.join(pkar.config.htmlgen.out_dir, "index.html")
    local ofh = assert(io.open(idx_path, "w"))

    logger:debug("Writing info at ", idx_path)
    ofh:write(out_html)
    ofh:close()

    return true
end


M.reset_site = function()
    -- Reset target folders.
    -- TODO for larger sites, a selective update should be implemented by
    -- comparing RDF resource timestamps with HTML page timestamps. Post-MVP.
    if path.isdir(pkar.config.htmlgen.out_dir) then
        logger:warn("Removing existing web site.")
        dir.rmtree(pkar.config.htmlgen.out_dir)
    end

    -- Recreate asset dir.
    if path.isdir(M.asset_dir) then
        logger:warn("Removing existing web assets.")
        dir.rmtree(M.asset_dir)
    end
    dir.makepath(M.asset_dir)

    -- Copy static assets.
    logger:info("Copying templates dir " .. datafile.path("templates/assets") .. " to " .. M.asset_dir)
    assert(dir.clonetree(
        datafile.path("templates/assets"),
        M.asset_dir, dir.copyfile)
    )
end


M.generate_site = function(keep)
    if not keep then M.reset_site() end

    -- Clear local search index keys.
    idx_keys = {
        id = true,
        content_type = true,
        type = true,
        fname = true,
    }

    -- Generate individual resource pages, RDF, and JSON index.
    assert(M.generate_resources())

    -- Generate index page.
    assert(M.generate_homepage())
end


return M