mirror of
https://github.com/littensy/charm.git
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110 lines
3.2 KiB
Text
110 lines
3.2 KiB
Text
local Charm = require("../Charm")
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local validate = require("./validate")
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local flags = Charm.flags
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--- A special symbol that denotes the absence of a value. Used to represent
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--- deleted values in patches.
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local None = { __none = "__none" }
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local function isNone(value: any): boolean
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return type(value) == "table" and value.__none == "__none"
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end
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--- JSON serialization can drop the last values of a sparse array. For example,
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--- `{ [1] = 1, [3] = 3 }` becomes `[1]` in some cases. Ambiguity in the
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--- serialization of sparse arrays can be resolved by converting them to
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--- dictionaries with string keys.
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---
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--- The `apply` function will convert these dictionaries back into arrays as
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--- long as the target array is not sparse. This function ensures that the diff
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--- function produces a patch that can be correctly applied.
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local function stringifySparseArray(object: { any }): { [string | number]: any }
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local maxn = table.maxn(object)
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if maxn == 0 or maxn == #object then
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-- The object is either not an array or a dense array
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return object
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end
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local dictionary = {}
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for index, value in next, object do
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dictionary[tostring(index)] = value
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end
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return dictionary
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end
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--- Compares two states and returns a patch that can be applied to the previous
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--- state to produce the next state.
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---
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--- @param prevState The previous state.
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--- @param nextState The next state.
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--- @param serialize Whether to convert sparse arrays into dictionaries. Defaults to `true`.
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--- @returns A patch that can be applied to the previous state.
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local function diff(prevState: { [any]: any }, nextState: { [any]: any }, serialize: boolean?)
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serialize = serialize ~= false
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local patches = table.clone(nextState)
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for key, previous in next, prevState do
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local current = nextState[key]
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if previous == current then
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patches[key] = nil
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elseif current == nil then
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patches[key] = None
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elseif type(previous) == "table" and type(current) == "table" then
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patches[key] = diff(previous, current, serialize)
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end
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end
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-- Coerce sparse array patches into dictionaries
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if serialize and (prevState[1] ~= nil or nextState[1] ~= nil) then
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patches = stringifySparseArray(patches)
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end
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if serialize and flags.strict then
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for key, value in next, patches do
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validate(value, key)
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end
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end
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return patches
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end
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--- Applies a patch to a state and returns the next state.
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---
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--- @param state The current state.
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--- @param patches The patches to apply.
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--- @returns The next state.
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local function apply(state: any, patches: any): any
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if type(patches) == "table" and patches.__none == "__none" then
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return nil
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elseif type(state) ~= "table" or type(patches) ~= "table" then
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return patches
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end
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local nextState = table.clone(state)
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local stateIsArray = state[1] ~= nil
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for key, patch in next, patches do
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-- Diff-checking an array produces a sparse array, which will not be
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-- preserved when converted to JSON. To prevent this, we turn string
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-- keys back into numeric keys.
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if stateIsArray and type(key) == "string" then
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key = tonumber(key) or key
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end
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nextState[key] = apply(nextState[key], patch)
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end
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return nextState
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end
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return {
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isNone = isNone,
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diff = diff,
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apply = apply,
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}
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