# Generation on the host's cryptographic source
# =============================================
#
# Generated identifiers and contexts on the host's cryptographic source:
# WebCrypto in JavaScript and the operating system's generator natively. They
# apply the rules of trace_context.bend: four words per trace ID candidate and
# two per span ID candidate, most significant first, eight candidates per
# identifier, no all-zero identifier, no reuse of an identifier to exclude,
# such as the parent's span ID or a received trace ID, and an immediate stop
# at the first source error. There is no time, counter or other fallback.
# TC.TraceId.generate_with, TC.Context.root_with and their siblings take a
# caller's source instead.
#
# The generation machine itself is pure: section 6 of LAWS.bend states its
# behavior over replayed tapes. This file only connects it, and the native
# HTTP shortcuts of native_http.bend, to the host source of entropy.bend.
#
# Every operation here relies on entropy.bend's foreign effect, so a check of
# a file that imports this module reports them and answers SOME PROOFS FAIL.
# No law imports it: the laws state the same operations on a caller's
# source, which is how PROOF.bend proves them without host code.

import Base
import ./trace_context.bend as TC
import ./native_http.bend as Adapter
import ./entropy.bend as Entropy

# The host source as the machine reads it: each read returns one word result
# from Entropy.read_u32, and the state is Unit because the host keeps none.
def Source.host(state: Unit) -> IO(Unit & Result<&1, &1, U32 & String, U32>):
  IO.bind(Result<&1, &1, U32 & String, U32>, Unit & Result<&1, &1, U32 & String, U32>,
    Entropy.read_u32(), word => IO.pure(Unit & Result<&1, &1, U32 & String, U32>, (state, word)))

# The host source has no state to hand back.
def on_host(-A: Type, action: IO(Unit & A)) -> IO(A):
  IO.bind(Unit & A, A, action, done => IO.pure(A, Pair.snd(Unit, A, done)))

# A trace ID alone, as an OpenTelemetry SDK generates one before its sampler
# decides on it (TC.TraceId.generate_with). It asserts random-trace-id and is
# never `excluded`, when there is one.
def TraceId.generate(excluded: Maybe<&2, TC.TraceId>) -> IO(Result<&2, &2, TC.GenerationError, TC.TraceId>):
  on_host(Result<&2, &2, TC.GenerationError, TC.TraceId>,
    TC.TraceId.generate_with(~Unit, ~Source.host, Unit{}, excluded))

# A span ID alone, as an SDK generates one once its sampler has decided, or
# for a child span with its parent's span ID excluded
# (TC.SpanId.generate_with).
def SpanId.generate(excluded: Maybe<&2, TC.SpanId>) -> IO(Result<&2, &2, TC.GenerationError, TC.SpanId>):
  on_host(Result<&2, &2, TC.GenerationError, TC.SpanId>,
    TC.SpanId.generate_with(~Unit, ~Source.host, Unit{}, excluded))

# Start a trace: a trace ID, then a span ID, as TC.Context.root_with composes
# them, with the sampled indication `sampled`, as it is given. The trace ID
# asserts random-trace-id, so the root is emitted with flags 03 when it is
# sampled and 02 when it is not: False gives an unsampled root, as
# Context.continue_or_start starts one by default.
def Context.root(sampled: Bool) -> IO(Result<&2, &2, TC.GenerationError, TC.LocalContext>):
  on_host(Result<&2, &2, TC.GenerationError, TC.LocalContext>,
    TC.Context.root_with(~Unit, ~Source.host, Unit{}, sampled))

# Continue a remote or local parent with a new operation.
def Context.child(parent: TC.Parent, sampling: TC.Sampling) -> IO(Result<&2, &2, TC.GenerationError, TC.LocalContext>):
  on_host(Result<&2, &2, TC.GenerationError, TC.LocalContext>,
    TC.Context.child_with(~Unit, ~Source.host, Unit{}, parent, sampling))

# Start a new trace instead of continuing a received context, with the
# sampled indication `sampled`, as a root takes it.
def Context.restart(previous: TC.RemoteContext, sampled: Bool) ->
  IO(Result<&2, &2, TC.GenerationError, TC.LocalContext>):
  on_host(Result<&2, &2, TC.GenerationError, TC.LocalContext>,
    TC.Context.restart_with(~Unit, ~Source.host, Unit{}, previous, sampled))

# Give a service its own operation for a received message: a child of the
# context that extraction keeps, the message's or the base, a root without
# one, or a new trace in its place at a trust boundary
# (TC.Context.continue_or_start_with).
def Context.continue_or_start(+extraction: TC.Extraction, reception: TC.Reception, sampling: TC.Sampling,
  +policy: TC.FailurePolicy) -> IO(TC.FailurePolicy.result(policy, TC.Service)):
  on_host(TC.FailurePolicy.result(policy, TC.Service),
    TC.Context.continue_or_start_with(~Unit, ~Source.host, Unit{}, extraction, reception, sampling, policy))

# Give one message that the service sends a new child of the service's
# operation, or the fallback when none can be generated
# (TC.Context.send_with).
def Context.send(+limits: TC.Limits, service: TC.Service, sampling: TC.Sampling, +policy: TC.FailurePolicy,
  +carrier: List<&2, TC.Header>) -> IO(TC.FailurePolicy.result(policy, TC.Sent)):
  on_host(TC.FailurePolicy.result(policy, TC.Sent),
    TC.Context.send_with(~Unit, ~Source.host, Unit{}, limits, service, sampling, policy, carrier))

# The service's own operation for a received request, from the header map of
# the request, on the host's cryptographic source: native_http.bend's
# continue_or_start_with on Source.host. `base` is the context to keep when
# the request carries no usable traceparent.
def NativeHttp.continue_or_start(+limits: TC.Limits, headers: Adapter.HeaderMap(), base: Maybe<&2, TC.BaseContext>,
  reception: TC.Reception, sampling: TC.Sampling, +policy: TC.FailurePolicy) ->
  IO(TC.FailurePolicy.result(policy, TC.Service)):
  on_host(TC.FailurePolicy.result(policy, TC.Service),
    Adapter.continue_or_start_with(~Unit, ~Source.host, Unit{}, limits, headers, base, reception, sampling, policy))

# Give one request that the service sends the context of a new operation, on
# the host's cryptographic source: native_http.bend's send_with on
# Source.host, which replaces the context fields of `headers`, the request's
# own header map.
def NativeHttp.send(+limits: TC.Limits, service: TC.Service, sampling: TC.Sampling, +policy: TC.FailurePolicy,
  headers: Adapter.HeaderMap()) -> IO(TC.FailurePolicy.result(policy, Adapter.Outbound)):
  on_host(TC.FailurePolicy.result(policy, Adapter.Outbound),
    Adapter.send_with(~Unit, ~Source.host, Unit{}, limits, service, sampling, policy, headers))