--[[
    generate and return text-based vertical histogram,
    with bins of given width across interval from max to min,
    transforming values to numbers via func,
    scaling bar-length by scale
]]
local function histogram(list, min, max, width, func, scale)
    local bins = {}
    local oorc = 0
    local prc = 0
    for _, v in ipairs(list) do
        local n = func(v)
        if n == n and n >= min and n < max + width then
            local k = math.floor((n - min) / width) + 1
            bins[k] = (bins[k] or 0) + 1
        else
            oorc = oorc + 1
        end
        prc = prc + 1
    end
    local s = ""
    for n = min, max, width do
        local k = math.floor((n - min) / width) + 1
        s = string.format("%s%.2f\t%s %d\n", s, n, ("\u{2588}"):rep(math.ceil(scale * (bins[k] or 0))), bins[k] or 0)
    end
    return s .. string.format("(%d out of range)\n", oorc)
end

local function fn(config, deck, deckfname, qs)
    local tcc = 0
    local tsc = 0
    local tfc = 0
    local spc = 0
    local expdeck = {}
    for _, card in ipairs(deck) do
        local rtc
        if not qs or card.note:find(qs) then
            rtc = true
            for _, pr in ipairs(card.pr) do
                tsc = tsc + pr.succ
                tfc = tfc + pr.fail
                if pr.delay < 0 then
                    spc = spc + 1
                else
                    table.insert(expdeck, pr)
                end
            end
        end
        if rtc then
            tcc = tcc + 1
        end
    end
    local qfn
    if qs then
        qfn = string.format(" (filtered with query %q)", qs)
    else
        qfn = ""
    end
    io.write(string.format(
        "%s%s has %d cards and %d total prompts\n",
        deckfname, qfn, tcc, #expdeck + spc
    ))
    io.write(string.format(
        "(average %.2f prompts per card, %d/%.1f%% prompts suspended).\n",
        (#expdeck + spc) / tcc, spc, 100 * spc / (#expdeck + spc)
    ))
    io.write(string.format(
        "The deck's prompts have been reviewed a total of %d times\n",
        tsc + tfc
    ))
    io.write(string.format(
        "(average %.2f reviews per prompt), overall retention %.2f%%.\n",
        (tsc + tfc) / (#expdeck + spc), 100 * tsc / (tsc + tfc)
    ))
    io.write("All further data excludes suspended prompts.\n")
    io.write("\nEase\n" .. histogram(expdeck, 1.0, 3.3, 0.1, function(pr) return pr.ease end, 0.03))
    io.write("\nLog2-delay (seconds)\n" .. histogram(expdeck, 15, 28, 0.5, function(pr) return math.log(pr.delay, 2) end, 0.1))
    io.write("\nDelay-last review ratio\n" .. histogram(expdeck, 0, 2, 0.1, function(pr) return (os.time() - pr.time) / pr.delay end, 0.1))
    io.write("\nRetention (%)\n" .. histogram(expdeck, 30, 100, 10, function(pr) return 100 * pr:retention() end, 0.02))
    io.write("\nReview counts\n" .. histogram(expdeck, 0, 20, 2, function(pr) return pr.succ + pr.fail end, 0.03))
    io.write("\nLog2-age (seconds)\n" .. histogram(deck, 18, 28, 0.5, function(card) return math.log(os.time() - (card.created or 2 * os.time()), 2) end, 0.05))
    io.write("\nPrompt-count\n" .. histogram(deck, 1, 10, 1, function(card) return #card.pr end, 0.03))
    local cpcs = {}
    for _, card in ipairs(deck) do
        local cp = card.note:match("([^:]+):") or ""
        cpcs[cp] = (cpcs[cp] or 0) + 1
    end
    local scl = {}
    for l, c in pairs(cpcs) do
        table.insert(scl, { l = l, c = c })
    end
    table.sort(scl, function(a, b) return a.c > b.c end)
    for k, lc in ipairs(scl) do
        scl[k] = string.format("%s (%d)", lc.l ~= "" and lc.l or "(none)", lc.c)
    end
    io.write("\nMost common contexts: " .. table.concat(scl, ", ", 1, math.min(20, #scl)) .. "\n")
    table.sort(expdeck, function(a, b) return a.time + a.delay < b.time + b.delay end)
    io.write("\nUpcoming due prompts wrt days from now:\n")
    local ppi = 1
    local mpi = 1
    for dc = 1,100 do
        for uc = ppi,#expdeck do
            if expdeck[uc].time + expdeck[uc].delay - os.time() > dc * 86400 then
                mpi = uc
                break
            end
        end
        if dc <= 10 or dc % 10 == 0 then
            io.write(string.format("%d\t%s %d\n", dc, ("\u{2588}"):rep(math.ceil((mpi - ppi) / 10)), mpi - ppi))
        end
        ppi = mpi
    end
end

return { desc = "(s)tatistics (with optional query)", nd = true, nq = true, fn = fn }