--[[
  [[ SHA-256 library for Halyde
  [[ Copyright (C) 2026  tema5002
  [[
  [[ This library is free software; you can redistribute it and/or
  [[ modify it under the terms of the GNU Library General Public
  [[ License as published by the Free Software Foundation; either
  [[ version 2 of the License, or (at your option) any later version.
  [[
  [[ This library is distributed in the hope that it will be useful,
  [[ but WITHOUT ANY WARRANTY; without even the implied warranty of
  [[ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  [[ Library General Public License for more details.
  [[
  [[ You should have received a copy of the GNU Library General Public
  [[ License along with this library; if not, see <https://www.gnu.org/licenses/>.
  ]]--
local sha256 = {}

local k = {
    0x428a2f98,0x71374491,0xb5c0fbcf,0xe9b5dba5,0x3956c25b,0x59f111f1,0x923f82a4,0xab1c5ed5,
    0xd807aa98,0x12835b01,0x243185be,0x550c7dc3,0x72be5d74,0x80deb1fe,0x9bdc06a7,0xc19bf174,
    0xe49b69c1,0xefbe4786,0x0fc19dc6,0x240ca1cc,0x2de92c6f,0x4a7484aa,0x5cb0a9dc,0x76f988da,
    0x983e5152,0xa831c66d,0xb00327c8,0xbf597fc7,0xc6e00bf3,0xd5a79147,0x06ca6351,0x14292967,
    0x27b70a85,0x2e1b2138,0x4d2c6dfc,0x53380d13,0x650a7354,0x766a0abb,0x81c2c92e,0x92722c85,
    0xa2bfe8a1,0xa81a664b,0xc24b8b70,0xc76c51a3,0xd192e819,0xd6990624,0xf40e3585,0x106aa070,
    0x19a4c116,0x1e376c08,0x2748774c,0x34b0bcb5,0x391c0cb3,0x4ed8aa4a,0x5b9cca4f,0x682e6ff3,
    0x748f82ee,0x78a5636f,0x84c87814,0x8cc70208,0x90befffa,0xa4506ceb,0xbef9a3f7,0xc67178f2
}

local function ROTRIGHT(a, b) return ((a >> b) | (a << (32 - b))) & 0xFFFFFFFF end
local function CH(x, y, z) return ((x & y) ~ ((~x) & z)) & 0xFFFFFFFF end
local function MAJ(x, y, z) return ((x & y) ~ (x & z) ~ (y & z)) & 0xFFFFFFFF end
local function EP0(x) return (ROTRIGHT(x, 2) ~ ROTRIGHT(x, 13) ~ ROTRIGHT(x, 22)) & 0xFFFFFFFF end
local function EP1(x) return (ROTRIGHT(x, 6) ~ ROTRIGHT(x, 11) ~ ROTRIGHT(x, 25)) & 0xFFFFFFFF end
local function SIG0(x) return (ROTRIGHT(x, 7) ~ ROTRIGHT(x, 18) ~ (x >> 3)) & 0xFFFFFFFF end
local function SIG1(x) return (ROTRIGHT(x, 17) ~ ROTRIGHT(x, 19) ~ (x >> 10)) & 0xFFFFFFFF end

local function sha256_transform(state, data)
    -- m = uint32_t[64]
    local m = {}
    
    -- convert to 32 bit BE words
    for i = 1, 16 do
        local j = (i - 1) * 4 + 1
        m[i] = (data[j] << 24) | (data[j+1] << 16) | (data[j+2] << 8) | data[j+3]
    end
  
    for i = 17, 64 do
        m[i] = (SIG1(m[i-2]) + m[i-7] + SIG0(m[i-15]) + m[i-16]) & 0xFFFFFFFF
    end
  
    local a, b, c, d, e, f, g, h = table.unpack(state)
    
    for i = 1, 64 do
        local t1 = (h + EP1(e) + CH(e,f,g) + k[i] + m[i]) & 0xFFFFFFFF
        local t2 = (EP0(a) + MAJ(a,b,c)) & 0xFFFFFFFF
        h, g, f, e, d, c, b, a = g, f, e, (d+t1)&0xFFFFFFFF, c, b, a, (t1+t2)&0xFFFFFFFF
    end

    state[1] = (state[1] + a) & 0xFFFFFFFF
    state[2] = (state[2] + b) & 0xFFFFFFFF
    state[3] = (state[3] + c) & 0xFFFFFFFF
    state[4] = (state[4] + d) & 0xFFFFFFFF
    state[5] = (state[5] + e) & 0xFFFFFFFF
    state[6] = (state[6] + f) & 0xFFFFFFFF
    state[7] = (state[7] + g) & 0xFFFFFFFF
    state[8] = (state[8] + h) & 0xFFFFFFFF
end

function sha256.init()
    return {
        state = {
            0x6a09e667,
            0xbb67ae85,
            0x3c6ef372,
            0xa54ff53a,
            0x510e527f,
            0x9b05688c,
            0x1f83d9ab,
            0x5be0cd19
        },
        buffer = {},
        buffer_len = 0,
        total_bits = 0
    }
end

function sha256.update(ctx, data)
    if type(data) ~= "string" then
        error("sha256.update expects string of bytes")
    end
    
    for i = 1, #data do
        local byte = string.byte(data, i)
        ctx.buffer[ctx.buffer_len + 1] = byte
        ctx.buffer_len = ctx.buffer_len + 1
        
        if ctx.buffer_len == 64 then
            sha256_transform(ctx.state, ctx.buffer)
            ctx.total_bits = ctx.total_bits + 512
            ctx.buffer_len = 0
            ctx.buffer = {}
        end
    end
end

function sha256.final(ctx)
    local bitlen = ctx.total_bits + (ctx.buffer_len * 8)
    local i = ctx.buffer_len + 1
    
    if ctx.buffer_len <= 55 then
        ctx.buffer[i] = 0x80
        for j = i + 1, 56 do
            ctx.buffer[j] = 0x00
        end
    else
        ctx.buffer[i] = 0x80
        for j = i + 1, 64 do
            ctx.buffer[j] = 0x00
        end
        sha256_transform(ctx.state, ctx.buffer)
        for j = 1, 56 do
            ctx.buffer[j] = 0x00
        end
    end
    
    ctx.buffer[57] = (bitlen >> 56) & 0xFF
    ctx.buffer[58] = (bitlen >> 48) & 0xFF
    ctx.buffer[59] = (bitlen >> 40) & 0xFF
    ctx.buffer[60] = (bitlen >> 32) & 0xFF
    ctx.buffer[61] = (bitlen >> 24) & 0xFF
    ctx.buffer[62] = (bitlen >> 16) & 0xFF
    ctx.buffer[63] = (bitlen >> 8) & 0xFF
    ctx.buffer[64] = bitlen & 0xFF
    
    sha256_transform(ctx.state, ctx.buffer)
    local result = {}
    for i = 0, 31 do
        result[i + 1] = (ctx.state[i//4 + 1] >> (24 - (i % 4) * 8)) & 0xFF
    end
    
    return result
end

function sha256.hash(data)
    local ctx = sha256.init()
    sha256.update(ctx, data)
    return sha256.final(ctx)
end

function sha256.to_hex(hash_bytes)
    local hex = {}
    for i = 1, #hash_bytes do
        hex[i] = string.format("%02x", hash_bytes[i])
    end
    return table.concat(hex)
end

function sha256.from_hex(hex_str)
    if #hex_str ~= 64 then
        error("invalid hex string length, expected 64 characters")
    end
    local bytes = {}
    for i = 1, 64, 2 do
        bytes[(i+1)/2] = tonumber(hex_str:sub(i, i+1), 16)
    end
    return bytes
end

return sha256